Formation, derivatization and applications of bacterial cellulose

Exploring Microemulsion Systems for the Incorporation of Glucocorticoids into Bacterial Cellulose: A Novel Approach for Anti-Inflammatory Wound Dressings

The effective pharmacological treatment of inflamed wounds such as pyoderma gangraenosum remains challenging, as the systemic application of suitable drugs such as glucocorticoids is compromised by severe side effects and the inherent difficulties of wounds as drug targets. Furthermore, conventional semi-solid formulations are not suitable for direct application to open wounds. Thus, the treatment of inflamed wounds could considerably benefit from the development of active wound dressings for the topical administration of anti-inflammatory drugs. Although bacterial cellulose appears to be an ideal candidate for this purpose due to its known suitability for advanced wound care and as a drug delivery system, the incorporation of poorly water-soluble compounds into the hydrophilic material still poses a problem. The use of microemulsions could solve that open issue. The present study therefore explores their use as a novel approach to incorporate poorly water-soluble glucocorticoids into bacterial cellulose. Five microemulsion formulations were loaded with hydrocortisone or dexamethasone and characterized in detail, demonstrating their regular microstructure, biocompatibility and shelf-life stability. Bacterial cellulose was successfully loaded with the formulations as confirmed by transmission electron microscopy and surprisingly showed homogenous incorporation, even of w/o type microemulsions. High and controllable drug permeation through Strat-M® membranes was observed, and the anti-inflammatory activity for permeated glucocorticoids was confirmed in vitro. This study presents a novel approach for the development of anti-inflammatory wound dressings using bacterial cellulose in combination with microemulsions.

Bacterial cellulose: A promising biopolymer with interesting properties and applications

The ever-increasing demands for materials with desirable properties led to the development of materials that impose unfavorable influences on the environment and the ecosystem. Developing a low-cost, durable, and eco-friendly functional material with biological origins has become necessary to avoid these consequences. Bacterial cellulose generated by bacteria dispenses excellent structural and functional properties and satisfies these requirements. BC and BC-derived materials are essential in developing pure and environmentally safe functional materials. This review offers a detailed understanding of the biosynthesis of BC, properties, various functionalization methods, and applicability in biomedical, water treatment, food storage, energy conversion, and energy storage applications.

A pilot and open trial to evaluate topical Bacterial Cellulose bio-curatives in the treatment of cutaneous leishmaniasis caused by L. braziliensis

The treatment of cutaneous leishmaniasis (CL) in Brazil using pentavalent antimony (Sb^v) is associated with a high failure rate and long time to heal. Moreover, standard Sb^v treatment cures only 50-60% of the cases. In this pilot clinical trial, we evaluated the topical use of bacterial cellulose (BC) bio-curatives + Sb^v in the treatment of CL caused by L. braziliensis, in Bahia, Brazil. A total of 20 patients were randomized in two groups assigned to receive either parenteral Sb^v alone or parenteral Sb^v plus topically applied BC bio-curatives. CL patients treated with Sb^v + topical BC bio-curatives had a significantly higher cure rate at 60 days post initiation of treatment compared to CL patients treated with Sb^v alone (P=0.01). At day 90 post initiation of treatment, cure rate was similar in the two groups as was overall healing time. Adverse effects or local reactions to topical BC application were not observed. This pilot trial shows that the potential use of a combined therapy consisting of topical BC bio-curatives and parenteral Sb^v in favoring healing of CL lesions caused by L. braziliensis, at an early time point.

Modified Bacterial Cellulose Dressings to Treat Inflammatory Wounds

Natural products suited for prophylaxis and therapy of inflammatory diseases have gained increasing importance. These compounds could be beneficially integrated into bacterial cellulose (BC), which is a natural hydropolymer applicable as a wound dressing and drug delivery system alike. This study presents experimental outcomes for a natural anti-inflammatory product concept of boswellic acids from frankincense formulated in BC. Using esterification respectively (resp.) oxidation and subsequent coupling with phenylalanine and tryptophan, post-modification of BC was tested to facilitate lipophilic active pharmaceutical ingredient (API) incorporation. Diclofenac sodium and indomethacin were used as anti-inflammatory model drugs before the findings were transferred to boswellic acids. By acetylation of BC fibers, the loading efficiency for the more lipophilic API indomethacin and the release was increased by up to 65.6% and 25%, respectively, while no significant differences in loading could be found for the API diclofenac sodium. Post-modifications could be made while preserving biocompatibility, essential wound dressing properties and anti-inflammatory efficacy. Eventually, in vitro wound closure experiments and evaluations of the effect of secondary dressings completed the study.

N-Doped Mo2C Nanobelts/Graphene Nanosheets Bonded with Hydroxy Nanocellulose as Flexible and Editable Electrode for Hydrogen Evolution Reaction

The large-scale application of economically efficient electrocatalysts for hydrogen evolution reaction (HER) is limited in view of the high cost of polymer binders (Nafion) for immobilizing of powder catalysts. In this work, nitrogen-doped molybdenum carbide nanobelts (N-Mo₂C NBs) with porous structure are synthesized through a direct pyrolysis process using the pre-prepared molybdenum oxide nanobelts (MoO₃ NBs). Nanocellulose instead of Nafion-bonded N-Mo₂C NBs (N-Mo₂C@NCs) exhibits superior performance toward HER, because of excellent dispersibility and multiple exposed catalytically active sites. Furthermore, the conductive film composed of N-Mo₂C NBs, graphene nanosheets, and nanocellulose (N-Mo₂C/G@NCs) is fabricated by simple vacuum filtration, as flexible and editable electrode, which possesses excellent performance for scale HER applications. This work not only proposes the potential of nanocellulose to replace Nafion for binding powder catalysts, but also offers a facile strategy to prepare flexible and conductive films for a wide variety of nanomaterials.

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N-Mo₂C nanobelts with porous structure are uniformly synthesized

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Nanocellulose is proposed to replace Nafion for binding powder catalysts

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A facile strategy to prepare conductive film electrode is offered with practice

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The flexible editable electrode exhibits excellent performance for scalable HER

Bacterial cellulose membrane functionalized with hydroxiapatite and anti-bone morphogenetic protein 2: A promising material for bone regeneration

Bone tissue engineering seeks to adequately restore functions related to physical and biological properties, aiming at a repair process similar to natural bone. The use of compatible biopolymers, such as bacterial cellulose (BC), as well as having interesting mechanical characteristics, presents a slow in vivo degradation rate, and the ability to be chemically modified. To promote better bioactivity towards BC, we synthesized an innovative BC membrane associated to hydroxyapatite (HA) and anti-bone morphogenetic protein antibody (anti-BMP-2) (BC-HA-anti-BMP-2). We present the physical-chemical, biological and toxicological characterization of BC-HA-anti-BMP-2. Presence of BC and HA components in the membranes was confirmed by SEM-EDS and FTIR assays. No toxic potential was found in MC3T3-E1 cells by cytotoxicity assays (XTT Assay and Clonogenic Survival), genotoxicity (Comet Assay) and mutagenicity (Cytokinesis-blocked micronucleus Test). The in vitro release kinetics of anti-BMP-2 antibodies detected gradually reducing antibody levels, reducing approximately 70% in 7 days and 90% in 14 days. BC-HA-anti-BMP-2 increased SPP1, BGLAP, VEGF, ALPL, RUNX2 and TNFRSF11B expression, genes involved in bone repair and also increased mineralization nodules and phosphatase alcalin (ALP) activity levels. In conclusion, we developed BC-HA-anti-BMP-2 as an innovative and promising biomaterial with interesting physical-chemical and biological properties which may be a good alternative to treatment with commercial BMP-2 protein.

Composite Gels Containing Whey Protein Fibrils and Bacterial Cellulose Microfibrils

In this study, we investigated the gelation of WPI fibrils in the presence of bacterial cellulose (BC) microfibrils at pH 2 upon prolonged heating. Rheology and microstructure were investigated as a function of BC microfibril concentration. The presence of BC microfibrils did not influence the gelation dynamics and resulting overall structure of the WPI fibrillar gel. The storage modulus and loss modulus of the mixed WPI‐BC microfibril gels increased with increasing BC microfibril concentration, whereas the ratio between loss modulus and storage modulus remained constant. The WPI fibrils and BC microfibrils independently form two coexisting gel networks. Interestingly, near to the BC microfibrils more aligned WPI fibrils seemed to be formed, with individual WPI fibrils clearly distinguishable. The level of alignment of the WPI fibrils seemed to be dependent on the distance between BC microfibrils and WPI fibrils. This also is in line with our observation that with more BC microfibrils present, WPI fibrils are more aligned than in a WPI fibrillar gel without BC microfibrils. The large deformation response of the gels at different BC microfibril concentration and NaCl concentration is mainly influenced by the concentration of NaCl, which affects the WPI fibrillar gel structures, changing form linear fibrillar to a particulate gel. The WPI fibrillar gel yields the dominant contribution to the gel strength.

An insight into nanocellulose as soft condensed matter: Challenge and future prospective toward environmental sustainability

Nanocellulose, a structural polysaccharide that has caught tremendous interests nowadays due to its renewability, inherent biocompatibility and biodegradability, abundance in resource, and environmental friendly nature. They are promising green nanomaterials derived from cellulosic biomass that can be disintegrated into cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC), relying on their sensitivity to hydrolysis at the axial spacing of disordered domains. Owing to their unique mesoscopic characteristics at nanoscale, nanocellulose has been widely researched and incorporated as a reinforcement material in composite materials. The world has been consuming the natural resources at a much higher speed than the environment could regenerate. Today, as an uprising candidate in soft condensed matter physics, a growing interest was received owing to its unique self-assembly behaviour and quantum size effect in the formation of three-dimensional nanostructured material, could be utilised to address an increasing concern over global warming and environmental conservation. In spite of an emerging pool of knowledge on the nanocellulose downstream application, that was lacking of cross-disciplinary study of its role as a soft condensed matter for food, water and energy applications toward environmental sustainability. Here we aim to provide an insight for the latest development of cellulose nanotechnology arises from its fascinating physical and chemical characteristic for the interest of different technology holders.

Structure of the Cellulose Synthase Complex of Gluconacetobacter hansenii at 23.4 Å Resolution

Bacterial crystalline cellulose is used in biomedical and industrial applications, but the molecular mechanisms of synthesis are unclear. Unlike most bacteria, which make non-crystalline cellulose, Gluconacetobacter hansenii extrudes profuse amounts of crystalline cellulose. Its cellulose synthase (AcsA) exists as a complex with accessory protein AcsB, forming a 'terminal complex' (TC) that has been visualized by freeze-fracture TEM at the base of ribbons of crystalline cellulose. The catalytic AcsAB complex is embedded in the cytoplasmic membrane. The C-terminal portion of AcsC is predicted to form a translocation channel in the outer membrane, with the rest of AcsC possibly interacting with AcsD in the periplasm. It is thus believed that synthesis from an organized array of TCs coordinated with extrusion by AcsC and AcsD enable this bacterium to make crystalline cellulose. The only structural data that exist for this system are the above mentioned freeze-fracture TEM images, fluorescence microscopy images revealing that TCs align in a row, a crystal structure of AcsD bound to cellopentaose, and a crystal structure of PilZ domain of AcsA. Here we advance our understanding of the structural basis for crystalline cellulose production by bacterial cellulose synthase by determining a negative stain structure resolved to 23.4 Å for highly purified AcsAB complex that catalyzed incorporation of UDP-glucose into β-1,4-glucan chains, and responded to the presence of allosteric activator cyclic diguanylate. Although the AcsAB complex was functional in vitro, the synthesized cellulose was not visible in TEM. The negative stain structure revealed that AcsAB is very similar to that of the BcsAB synthase of Rhodobacter sphaeroides, a non-crystalline cellulose producing bacterium. The results indicate that the crystalline cellulose producing and non-crystalline cellulose producing bacteria share conserved catalytic and membrane translocation components, and support the hypothesis that it is the extrusion mechanism and order in linearly arrayed TCs that enables production of crystalline cellulose.

Microstructure and rheology of microfibril-polymer networks

By using an adsorbing polymer in combination with mechanical de-agglomeration, the microstructure and rheological properties of networks of microfibrils could be controlled. By the addition of sodium carboxymethyl cellulose during de-agglomeration of networks of bacterial cellulose, the microstructure could be changed from an inhomogeneous network with bundles of microfibrils and voids to a more homogeneous spread and alignment of the particles. As a result the macroscopic rheological properties were altered. Although still elastic and gel-like in nature, the elasticity and viscous behavior of the network as a function of microfibril concentration is altered. The microstructure is thus changed by changing the surface properties of the building blocks leading to a direct influence on the materials macroscopic behavior.

Preparation of Bacterial Cellulose/Inorganic Gel of Bentonite Composite by In Situ Modification

To evaluate the possibility of Bacterial cellulose/Inorganic Gel of Bentonite (BC/IGB) composite production using in situ method, the BC/IGB composite was successfully produced by in situ modification of BC in both HS medium and corncob hydrolysate. The results showed that the BC/IGB composite obtained in HS medium (one classical medium for BC production) had a higher water holding capacity, but the water retention capacity of the BC/IGB composite obtained in corncob hydrolysate was better. The performance of BC/IGB composite depended on the environment of in situ modification. Using different media showed significant influence on the sugar utilization and BC yield. In addition, BC/IGB composite produced by in situ method was compared with that produced by ex situ method, and the results shows that water holding capacity of BC/IGB composite obtained through in situ method was better. XRD results showed the crystallinity of BC/IGB composite related little to its performance as water absorbent. Overall, in situ modification is appropriate for further production of BC composite and other clay materials.

Phase transitions in cellulose microfibril dispersions by high-energy mechanical deagglomeration

It is shown that dispersions of cellulose microfibrils display gel-sol and direct gel-colloidal liquid crystalline structure transitions. This is achieved by applying high-energy mechanical deagglomeration to bacterial cellulose (BC) networks in the presence of sodium carboxymethyl cellulose (CMC). At high CMC content adsorption of the polymer leads to a significant increase in the ζ potential. The resulting apparent phase diagram shows transitions from aggregates to single microfibril dispersions with increasing the CMC/BC weight ratio at low microfibril concentrations. At higher concentrations, liquid crystalline ordering was observed and the microstructure becomes more homogeneous with increasing the CMC content. The observed liquid crystalline ordering was found to be reminiscent of nematic gels. Applying deagglomeration in the presence of CMC, thus, transitions the system from aggregates and gels to dispersions of single microfibrils and nematic gel-type structures.

A novel biomaterial: bacterial cellulose and its new era applications

Bacterial cellulose (BC) is a promising natural polymer that is produced by bacteria and that has unique and desirable structural, physical, and chemical properties. From the time when the remarkable properties of BC were found 15 years ago compared with plant cellulose, interest has grown in BC and it has become an article of trade in diverse applications. Following this trend, this paper reviews the progress of relevant studies, including general information about cellulose, production by microorganisms as well as BC cultivation, and its properties. The applications reviewed in the present article comprise biological and nonbiological fields. The latest use of BC in the biomedical, environmental, agricultural, electronic, food, and industrial fields is discussed with its applications in composite form. The present article attempts to amass the assorted uses of BC under one umbrella. Thus, recent advances in BC applications in different fields are thoroughly reviewed. This article concludes with the need for future research of BC to make it commercialized as vital biomaterial.

On the non-linear attachment characteristics of blood to bacterial cellulose/kaolin biomaterials

In this communication, we report a non-linear variation in the strength of blood attachment to bacterial cellulose/kaolin biomaterials as the fractions of bacterial cellulose to kaolin are increased. The changes observed for attachment strength are elucidated following both experimental and numerical investigations on both the biomaterial and the blood-biomaterial interface. Our research reveals that the non-linear strength of attachment of blood is related to topographical characteristics on the surface of the biomaterial, the maleability of the biomaterial and the intermolecular strength of attraction between clotted blood proteins (fibrinogen) with the cellulose/kaolin components of the biomaterial.

Antimicrobial Brazilian Propolis (EPP-AF) Containing Biocellulose Membranes as Promising Biomaterial for Skin Wound Healing

Among remarkable discoveries concerning propolis, such as antifungal, antiviral, and antioxidant activities, its anti-inflammatory, and mainly its antibacterial, properties deserve special attention when skin wound healing is concerned. Based on this and knowing the distinctive performance of bacterial (BC) membranes on wound healing, in this work it is proposed to demonstrate the potent antimicrobial activity and wound healing properties of a novel propolis containing biocellulose membrane. The obtained propolis/BC membrane was able to adsorb propolis not only on the surface, but also in its interstices demonstrated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, and thermogravidimetric assays. Additionally, the polyphenolic compounds determination and the prominent antibacterial activity in the membrane are demonstrated to be dose dependent, supporting the possibility of obtaining propolis/BC membranes at the desired concentrations, taking into consideration its application and its skin residence time. Finally, it could be suggested that propolis/BC membrane may favor tissue repair in less time and more effectively in contaminated wounds.

Production of microbial cellulose by a bacterium isolated from fruit

This study presents the production of bacterial cellulose (BC) by a bacterium isolated from a rotten fruit and its process optimization. Here, isolation and screening of potent cellulose producers were carried out from different natural sources, viz., soil, rotten fruits, and vegetables and vinegar. A total of 200 bacterial isolates were obtained, which were screened for cellulose production using Hestrin-Schramm medium. A novel and potent cellulose-producing bacterium was newly isolated from a rotten fruit and identified as Gluconacetobacter sp. F6 through 16S ribosomal DNA sequencing and morphological, cultural, and biochemical characteristics. After optimization of culture conditions, including pH, temperature, agitation, carbon/nitrogen sources, and inducers, the BC production was greatly increased from 0.52 to 4.5 g/l (8.65-fold increase). The optimal culture medium contained 1% (w/v) glucose, 1.5% (w/v) yeast extract, 0.5% (w/v) peptone, 0.27% (w/v) disodium hydrogen phosphate, 0.115% (w/v) citric acid, and 0.4% (w/v) ethanol. BC produced was analyzed for the presence of cellulose fibrils by epiflourescent microscopy using Calcofluor white stain and scanning electron microscopy and confirmed by NMR. There are very scanty reports about the optimization of BC production by bacteria isolated from rotten fruits.

Improvement of bacterial cellulose production by addition of agar in a jar fermentor

Bacterial cellulose (BC) was produced by Acetobacter xylinum BPR 2001 and its acetan nonproducing mutant EP1 in corn steep liquor-fructose medium in a 10-l jar fermentor supplemented with different agar concentrations ranging from 0% to 1.0% (w/v). The BC productivity of the two strains was increased by adding agar. The maximum BC production of BPR 2001 at an agar concentration of 0.4% was 12.8 g/l compared with 8 g/l without agar. The mutant EP1 produced 11.6 g/l of BC at an agar concentration of 0.6%, while only 5.5 g/l was produced in the control. Enhanced productivity is associated with an increase in viscosity of the culture, dispersion of BC pellets, and number of free cells due to agar addition, suggesting that acetan produced by BPR 2001 has a critical role in enhanced BC production.

Statistical optimization of culture conditions for bacterial cellulose production using Box-Behnken design

Culture conditions in a jar fermentor for bacterial cellulose (BC) production from A. xylinum BPR2001 were optimized by statistical analysis using Box-Behnken design. Response surface methodology was used to predict the levels of the factors, fructose (X1), corn steep liquor (CSL) (X2), dissolved oxygen (DO) (X3), and agar concentration (X4). Total 27 experimental runs by combination of each factor were carried out in a 10-L jar fermentor, and a three-dimensional response surface was generated to determine the effect of the factors and to find out the optimum concentration of each factor for maximum BC production and BC yield. The fructose and agar concentration highly influenced the BC production and BC yield. However, the optimum conditions according to changes in CSL and DO concentrations were predicted at almost central values of tested ranges. The predicted results showed that BC production was 14.3 g/L under the condition of 4.99% fructose, 2.85% CSL, 28.33% DO, and 0.38% agar concentration. On the other hand, BC yield was predicted in 0.34 g/g under the condition of 3.63% fructose, 2.90% CSL, 31.14% DO, and 0.42% agar concentration. Under optimized culture conditions, improvement of BC production and BC yield were experimentally confirmed, which increased 76% and 57%, respectively, compared to BC production and BC yield before optimizing the culture conditions.

Palladium-bacterial cellulose membranes for fuel cells

Bacterial cellulose is a versatile renewable biomaterial that can be used as a hydrophilic matrix for the incorporation of metals into thin, flexible, thermally stable membranes. In contrast to plant cellulose, we found it catalyzed the deposition of metals within its structure to generate a finely divided homogeneous catalyst layer. Experimental data suggested that bacterial cellulose possessed reducing groups capable of initiating the precipitation of palladium, gold, and silver from aqueous solution. Since the bacterial cellulose contained water equivalent to at least 200 times the dry weight of the cellulose, it was dried to a thin membranous structure suitable for the construction of membrane electrode assemblies (MEAs). Results of our study with palladium-cellulose showed that it was capable of catalyzing the generation of hydrogen when incubated with sodium dithionite and generated an electrical current from hydrogen in an MEA containing native cellulose as the polyelectrolyte membrane (PEM). Advantages of using native and metallized bacterial cellulose membranes in an MEA over other PEMs such as Nafion 117 include its higher thermal stability to 130 degrees C and lower gas crossover.

Molecular biology of cellulose production in bacteria

Cellulose biosynthesis has recently been established for a variety of bacteria of diverse origin at the phenotypic and genetic levels. Novel regulatory pathways, which involve the second messenger bis-(3',5') cyclic diguanylic acid and several proteins with the GGDEF domain, participate in the regulation of cellulose biosynthesis. The biological significance of cellulose production in environmental, commensal and pathogenic bacteria is only punctually resolved. This review summarizes current knowledge on cellulose biosynthesis, its regulation and biological function.

Phosphodiesterase A1, a regulator of cellulose synthesis in Acetobacter xylinum, is a heme-based sensor

The phosphodiesterase A1 protein of Acetobacter xylinum, AxPDEA1, is a key regulator of bacterial cellulose synthesis. This phosphodiesterase linearizes cyclic bis(3'-->5')diguanylic acid, an allosteric activator of the bacterial cellulose synthase, to the ineffectual pGpG. Here we show that AxPDEA1 contains heme and is regulated by reversible binding of O(2) to the heme. Apo-AxPDEA1 has less than 2% of the phosphodiesterase activity of holo-AxPDEA1, and reconstitution with hemin restores full activity. O(2) regulation is due to deoxyheme being a better activator than oxyheme. AxPDEA1 is homologous to the Escherichia coli direct oxygen sensor protein, EcDos, over its entire length and is homologous to the FixL histidine kinases over only a heme-binding PAS domain. The properties of the heme-binding domain of AxPDEA1 are significantly different from those of other O(2)-responsive heme-based sensors. The rate of AxPDEA1 autoxidation (half-life > 12 h) is the slowest observed so far for this type of heme protein fold. The O(2) affinity of AxPDEA1 (K(d) approximately 10 microM) is comparable to that of EcDos, but the rate constants for O(2) association (k(on) = 6.6 microM(-)(1) s(-)(1)) and dissociation (k(off) = 77 s(-)(1)) are 2000 times higher. Our results illustrate the versatility of signal transduction mechanisms for the heme-PAS class of O(2) sensors and provide the first example of O(2) regulation of a second messenger.

Synthesis and cytotoxic evaluation of cycloheximide derivatives as potential inhibitors of FKBP12 with neuroregenerative properties

On the basis of the new finding that the protein synthesis inhibitor cycloheximide (1, 4-[2-(3, 5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl]-2,6-piperidinedione) is able to competitively inhibit hFKBP12 (K(i) = 3.4 microM) and homologous enzymes, a series of derivatives has been synthesized. The effect of the compounds on the activity of hFKBP12 and their cytotoxicity against eukaryotic cell lines (mouse L-929 fibroblasts, K-562 leukemic cells) were determined. As a result, several less toxic or nontoxic cycloheximide derivatives were identified by N-substitution of the glutarimide moiety and exhibit IC(50) values in the range of 22.0-4.4 microM for inhibition of hFKBP12. Among these compounds cycloheximide-N-(ethyl ethanoate) (10, K(i) = 4.1 microM), which exerted FKBP12 inhibition to an extent comparable to that of cycloheximide (1), was found to cause an approximately 1000-fold weaker inhibitory effect on eukaryotic protein synthesis (IC(50) = 115 microM). Cycloheximide-N-(ethyl ethanoate) (10) was able to significantly speed nerve regeneration in a rat sciatic nerve neurotomy model at dosages of 30 mg/kg.

Active-site mutations which change the substrate specificity of the Clostridium stercorarium cellulase CelZ implications for synergism

CelZ from the cellulolytic thermophile Clostridium stercorarium has been described as a 'monomeric' cellulase able to effect both the endoglucanolytic hydrolysis of internal glycosidic linkages and the exoglucanolytic degradation from the chain ends in a processive mode of action. The putative catalytic residues of this family 9 cellulase, Asp84 and Glu447 located within the N-terminal domain of the modular protein, were replaced by site-directed mutagenesis. A minimized CelZ derivative (CelZC') comprising the catalytic domain and the adjacent cellulose-binding domain (CBD) family IIIc domain C' was used as target for mutagenesis. Six mutant enzymes and the unmodified CelZC' protein were purified to homogeneity and compared with respect to thermoactivity, substrate specificity, product profile and synergism. CD studies revealed that no major changes to the overall structure of the proteins had occurred. Replacement of either one or both catalytic residues completely eliminated the ability of CelZ to attack insoluble Avicel preparations indicative of the exo-activity, whereas the endo-activity measured via hydrolysis of CM-cellulose was retained upon substitution of the catalytic base Asp84. Thus, endo-active CelZ mutants defective in the exo-activity were available for co-operativity studies with the C. stercorarium exoglucanase CelY. Synergism was found to be dependent on the endo-activity of CelZ. Mutants Asp84Gly and Asp84Glu were able to enhance the degradation of crystalline cellulose significantly, although no products could be released from this substrate by individual action of the mutants.